An iPod is a financial black hole, designed to combat the problem of money becoming concentrated around individual people. Them iPod works via the capitalist interaction, which can be thought of as one of the five fundamental interactions (along with the gravity, strong, electromagnetic and weak interactions). The iPod absorbs money from entities possessing large amounts of it, and slowly emits the energy contained in the money as molecular vibrations. During this process, the energy contained in the battery power of the iPod is also emitted as molecular vibrations, and when this reaches zero, the functionality of the iPod disappears.
The field strength per dollar of an iPod is given by the following equation:
Field strength per dollar = - iPod capacity / (4 * pi * permittivity of free space * (distance between iPod and money)^2)
where iPod capacity is measured in gibibytes, and distance in metres.
Little Johnny has $40. His wallet is 1 metre away from an iPod. The iPod has a capacity of 40 GiB. Using the formula, Little Johnny's money is subjected to a force of magnitude approximately 10^13 Newtons by the iPod. No wonder he wouldn't shut up asking for one.